1. Field of the Invention
This invention relates to certain glass-filled adhesive and/or sealant compositions having improved ability to resist degradation caused by thermal cycling.
2. Prior Art
Adhesive and sealant compositions based on acrylate and alkylacrylate monomers polymerizable by free-radical initiation are known in the art. Likewise, anaerobic compositions are known in the art (see, for example, U.S. Pat. Nos. 2,895,950, 3,043,820 and 3,218,305). Anaerobic compositions are characterized by their ability to remain liquid in the presence of air, but cure to a strong adhesive bond when air is excluded, as by assembling a mated nut and bolt to which the composition has been applied.
While serving many useful purposes, both standard acrylate compositions as well as anaerobic-type acrylate compositions have been limited in applicability due to degradation of adhesive strength caused by wide cyclical fluctuations in temperature, e.g., in the range of -50.degree. to +180.degree. F. or more.
It is well known in the art that various improvements in the properties of polymer compositions may be effected by inclusion in the composition of one or more inorganic fillers. Over the years, glass has proven to be a particularly useful and desirable filler because of its chemical inertness, relative cheapness, and resistance to water absorption, among others. Glass is available in a variety of forms, e.g., solid spheres or beads, hollow spheres or microballoons, nodules, flakes, powder and milled fibers. Each form tends to produce certain properties or has certain special uses. For example, beads tend to improve strength properties, abrasion resistance and dimensional stability; microballoons significantly reduce the bulk density of the filled composition; flakes provide moisture and corrosion resistance as well as decorativeness; fibers tend to increase some strength properties. For a more detailed treatment of filler technology, reference may be made to any of the numerous texts dealing with, e.g., thermoplastics, thermosets, molding, and adhesives; for instance, "Modern Plastics Encyclopedia," published annually by McGraw-Hill, Inc., New York, New York.